1. Field of the Invention
The present invention relates to the manufacture of cast contact lenses with particular reference to controlling lens sizes independently of mold size.
2. Description of the Prior Art
Contact lenses are being made of "soft" materials, e.g. silicone resins, by casting them in split molds. U.S. Pat. Nos. 3,761,208 and 3,915,609 are exemplary. The molds are provided with casting surfaces having the curved shapes, diameters and high optical polish needed to produce the desired optical and physical parameters. Heretofore, each different lens prescription has required a different pair of costly and difficult to make mold halves rendering cast contact lens production less than optimally efficient, tedious and overly expensive.
With a view to overcoming the aforesaid and corollary drawbacks of current contact lens casting operations, it is an object of the present invention to provide for the casting of a multiplicity of lens sizes from a single pair of casting mold halves by adding an extractable diluent to the casting precursor and extracting the diluent after casting. By judicious use of the diluent, finished cast lens sizes smaller than casting cavity size can be reliably regulated.
While the prior art, e.g. U.S. Pat. No. 3,496,254, suggests that rigid contact lenses can be soaked in swelling agents for increasing their size and rendering them flexible, the ultimate size of such lenses can only be regulated by control of the casting cavity size, i.e. a different casting cavity for each change in finished lens size, and the aforementioned problems of prior art lens casting inefficiencies, tediousnesses and high cost remain. Control of lens size according to the present invention with a precursor diluent and its ultimate extraction instead of mold size changes, avoids these problems and drawbacks.
Other advantages of the invention will become apparent from the following description.